1. Field of the Invention
The present invention relates generally to mobile communication systems, and more particularly, to a method and device for optimizing an operating point of a power amplifier in a WCDMA (Wideband Code Division Multiple Access) mobile terminal.
2. Description of the Related Art
In a recent mobile communication system, a next-generation portable telephone system based on a WCDMA (Wideband Code Division Multiple Access) standard, as proposed by the 3GPP (Third Generation Partnership Project), using a spread spectrum scheme has proceeded toward commercialization in order to further improve frequency usage efficiency. The linearity required to transmit a signal specified in the 3GPP WCDMA standard dictates the use of a linear power amplifier (which means its operating point is setup in class A or, with some precautions, in class AB) in mobile terminals. The 3GPP WCDMA standard expresses the linearity requirements in specifying an output power spectrum mask of the mobile terminal as presented in FIG. 1.
However, the linear power amplifier consumes a relatively large amount of DC power. For example, a class A amplifier comprising 2 MESFET stages employing GaAs technology consumes 450 mA with a power supply of 5V to deliver a peak output power level (usually expressed by the compression point at 1 dB) of +30dBm with 20dB of gain. In the typical case of a mobile terminal, the power amplifier""s power supply consumption represents at least 70% of the total power consumption of the mobile terminal during transmission mode. Thus, it is critical to control an operating point, e.g., a bias current, of the power amplifier to decrease as much as possible its power consumption, while respecting the linearity requirement.
Accordingly, it would be desirable and highly advantageous to have a device and method of optimizing an operating point of a power amplifier in a WCDMA (Wideband Code Division Multiple Access) mobile terminal as to reduce power consumption and conserve battery life of the mobile terminal.
The problems stated above, as well as other related problems of the prior art, are solved by the present invention, a device and method of optimizing an operating point of a power amplifier in a WCDMA (Wideband Code Division Multiple Access) mobile terminal. The operating point of the power amplifier is defined by its bias current.
The device and method of the present invention reduces power consumption of a power amplifier, e.g., by optimizing its operating point or bias current, by using a combination of three signals received by the mobile terminal: (1) TFCI (Transport Format Combination Indicator) information; (2) compressed mode information; and (3) required output power level information. The three signals are then used by a digital processor to read from a memory a stored optimized operating point value, i.e., a bias current, which is supplied to a power amplifier of a mobile terminal during transmission mode.
According to one aspect of the present invention, a method for optimizing an operating point of a power amplifier in a mobile terminal is provided, the method including the steps of receiving a first signal from a base transceiver station; determining a Transport Format Combination Indicator (TFCI) value from the first signal; determining a status of a compressed mode of the mobile terminal, the status of the compressed mode being determined by the first signal; determining a required power output level of the mobile terminal, the required power output level being determined by the first signal; reading an operating point value from a memory in response to the TFCI value, the compressed mode status and the required power output level; and supplying the operating point value to the power amplifier. The operating point value is indicative of a bias current.
According to another aspect of the present invention, in a mobile communication system including a plurality of base transceiver stations, a mobile communication terminal is provided including an antenna for receiving a first control signal from at least one base transceiver station; a processor for determining a Transport Format Combination Indicator (TFCI) value, a compressed mode status, and a required power output level from the first control signal; a state machine for retrieving from a memory an operating point value of a power amplifier in response to the TFCI value, the compressed mode status, and required output level; and the power amplifier for amplifying a transmission signal to be transmitted through the antenna.